The present invention relates to a heated nozzle for plastic injection molding and that is incorporated into an injection molding machine and a manufacturing method therefor.
As shown in FIGS. 4 and 5, this type of heated nozzle for plastic injection molding is provided with a coil-shaped heater 3 and a cylinder 4 external to the surface of the outer periphery of the cavity sleeve portion 2 of the heated nozzle main unit 1. The heat that is generated from the heated coil-shaped heater 3 and in the direction indicated by the arrow (See FIG. 4) heats the cavity sleeve portion 2 of the heated nozzle main unit 1 so that the molten plastic material that passes through the passage 5 provided to the cavity sleeve portion 2 is maintained within the allowable temperature range.
With such a heated nozzle for plastic injection molding, the heat that is generated from the coil-shaped heater 3 is transmitted to the cavity sleeve portion 2 via the contact surface between the cavity sleeve portion 2 and the inner surface of the coil-shaped heater 3 and the contact surface area is a factor for increasing the ratio of thermal conductivity but there is a structural limit to the degree to which the contact surface area can be made larger, and so there is a limit to the degree to which the ratio of thermal conductivity can be made larger. Because of this, heating the cavity sleeve portion 2 to the required temperature involves raising the temperature of the coil-shaped heater 3, but raising the temperature of the coil-shaped heater 3 shortens the life of the coil-shaped heater 3 and results in less years of use.